We have purified somatomedin-C (SM-C) to about 90% homogeneity. We plan to commit about 100 micrograms of this material in an attempt to prepare monoclonal antibodies. Our hope is to isolate larger amounts of SM-C from plasma. This will entail coupling of the antibody to an immobile support. We also plan to develop an in vitro system which responds to SM-C. In this project freshly isolated chondrocytes of neonatal rats will be used. Using this specialized tissue, we plan (a) to probe the metabolic actions of SM-C in vitro and (b) to glean some information regarding its mechanism of action. We will use a SM-C preparation of lesser purity than that employed for the antibody project. The former preparation is about 50% pure. In the studies alluded to under (b), we will use (125I-iodo) SM-C which will be radiolabeld by a reagent "iodogen." This reagent is much more mild than chloramine T and acceptably high specific activities have been obtained.